Viewing Digital Slides

1. A system for collaborative viewing of a digital slide image, comprising a plurality of randomly-accessible blocks stored in a memory, the system comprising: at least one hardware processor; a region cache; a block cache that is logically distinct from the region cache; and at least one executable software module that, when executed by the at least one hardware processor, establishes a session for viewing at least a portion of a digital slide image by a plurality of client viewers, wherein the digital slide image comprises an image of a specimen on a microscope slide and is associated with a plurality of discrete individually-toggleable annotation layers, wherein each of the plurality of annotation layers comprises one or more annotations, identifies a leader client viewer and one or more non-leader client viewers from the plurality of client viewers, tracks navigation movements on the at least a portion of the digital slide image being viewed, while tracking the navigation movements, constructs a region, to be viewed as the at least a portion of the digital slide image, from two or more of the plurality of randomly-accessible blocks, stores the constructed region in the region cache, stores, in the block cache, each of the two or more randomly-accessible blocks that is used to construct the region, pre-fetches, from the memory, one or more of the plurality of randomly-accessible blocks that have not yet been accessed for viewing during the session based on a direction of the navigation movements, and stores, in the block cache, the pre-fetched one or more randomly-accessible blocks, receives a command from the leader client viewer, wherein the command comprises an interaction to toggle one or more of the plurality of annotation layers between enabled and disabled, and, in response to receiving the command from the leader client viewer, sends a command to each of the non-leader client viewers to synchronize a view of the at least a portion of the digital slide image at the one or more non-leader client viewers with the view of the at least a portion of the digital slide image at the leader client viewer by toggling the one or more of the plurality of annotation layers between enabled and disabled in accordance with the command from the leader client viewer.

2. The system of claim 1 , wherein the at least one executable software module further: receives a request to establish the session from a first one of the plurality of client viewers; in response to the request, establishes the session; and identifies the first client viewer as the leader client viewer.

3. The system of claim 1 , wherein the at least one executable software module further: receives a request to establish a new leader client viewer from the leader client viewer; and, in response to the request, identifies a new leader client viewer.

4. The system of claim 3 , wherein identifying a new leader client viewer comprises identifying one of the one or more non-leader client viewers selected by the leader client viewer.

5. The system of claim 3 , wherein identifying a new leader client viewer comprises selecting a client viewer from a queue of one or more non-leader client viewers that have requested to become leader.

6. The system of claim 1 , wherein the system further comprises a session table comprising a status for each of the plurality of client viewers.

7. The system of claim 1 , further comprising a database, wherein the one or more annotations in the plurality of annotation layers are stored in the database as a simple string.

8. The system of claim 1 , wherein the at least one executable software module further scales one or more of the annotations to a resolution of the digital slide image.

9. A method for collaborative viewing of a digital slide image, comprising a plurality of randomly-accessible blocks stored in a memory, the method comprising using at least one hardware processor to: establish a session for viewing at least a portion of a digital slide image by a plurality of client viewers, wherein the digital slide image comprises an image of a specimen on a microscope slide and is associated with a plurality of discrete individually-toggleable annotation layers, wherein each of the plurality of annotation layers comprises one or more annotations; identify a leader client viewer and one or more non-leader client viewers from the plurality of client viewers; track navigation movements on the at least a portion of the digital slide image being viewed; while tracking the navigation movements, construct a region, to be viewed as the at least a portion of the digital slide image, from two or more of the plurality of randomly-accessible blocks, store the constructed region in the region cache, store, in a block cache that is logically distinct from the region cache, each of the two or more randomly-accessible blocks that is used to construct the region, pre-fetch, from the memory, one or more of the plurality of randomly-accessible blocks that have not yet been accessed for viewing during the session based on a direction of the navigation movements, and store, in the block cache, the pre-fetched one or more randomly-accessible blocks; receive a command from the leader client viewer, wherein the command comprises an interaction to toggle one or more of the plurality of annotation layers between enabled and disabled; and, in response to receiving the command from the leader client viewer, send a command to each of the non-leader client viewers to synchronize a view of the at least a portion of the digital slide image at the one or more non-leader client viewers with the view of the at least a portion of the digital slide image at the leader client viewer by toggling the one or more of the plurality of annotation layers between enabled and disabled in accordance with the command from the leader client viewer.

10. The method of claim 9 , further comprising: receiving a request to establish the session from a first one of the plurality of client viewers; in response to the request, establishing the session; and identifying the first client viewer as the leader client viewer.

11. The method of claim 9 , further comprising: receiving a request to establish a new leader client viewer from the leader client viewer; and, in response to the request, identifying a new leader client viewer.

12. The method of claim 11 , wherein identifying a new leader client viewer comprises identifying one of the one or more non-leader client viewers selected by the leader client viewer.

13. The method of claim 11 , wherein identifying a new leader client viewer comprises selecting a client viewer from a queue of one or more non-leader client viewers that have requested to become leader.

14. The method of claim 9 , further comprising maintaining a session table comprising a status for each of the plurality of client viewers.